Apparatus for attaching soft tissue to bone

ABSTRACT

An anchor for attaching soft tissue to a bone comprising a head having a central dome with a suture bore extending therethrough. The dome includes a pair of substantially flat, oppositely disposed lands configured for engagement to a driving tool for inserting the anchor into the bone. A shaft extend from the head, and includes a first series of helical threads having a first diameter, and second series of helical threads interleaved with the first series of threads. The second series of threads has a diameter substantially different than the first diameter. The anchor employs a guide wire bore extending along the length of the anchor shaft.

TECHNICAL FIELD

The present invention relates generally to apparatus for attaching softtissue to bone, and more particularly to a bone anchor which functionsas an attachment site for sutures used to retain soft tissue in intimatecontact with a bone to permit reattachment of the soft tissue to thebone.

BACKGROUND ART AND TECHNICAL PROBLEM

The principal components of a skeletal system, for example a humanskeletal system, include bones which comprise the framework for thebody, cartilage which forms the connecting and supporting structuresamong the bones, and ligaments which bind the bones together. When aligament becomes detached from a bone, for example due to an athletic orother injury, it is often desirable to reattach the ligament to thebone.

Ligaments and other soft tissue (e.g., tendons) may be reattached to abone in a number of different ways. For example, Goble et al., U.S. Pat.No. 5,013,316, issued May 7, 1991, discloses a soft tissue anchorcomprising a footing stud that includes a drill and followed by selftapping threads, wherein the footing stud is arranged for turning andtapping into a bone mass. A longitudinal hole is disposed within thefooting stud and is configured to receive and retain therein a tackwhich includes an undersurface comprising spikes for engaging andpenetrating a ligament. When the tack is urged into the bore of thefooting stud, the spikes engage the soft tissue and maintain it inintimate contact with the bone.

Goble et al., U.S. Pat. No. 4,738,255, issued Apr. 19, 1989, discloses asuture anchor system that includes a drill and guide arrangement fordrilling an opening into a bone mass which is outwardly flared toaccommodate a suture anchor dispensed from an applicator, which sutureanchor is configured to be expanded within the bone mass to secure theanchor within the undersurface of the bone. As tension is applied to thesuture, the anchor remains underneath the surface of the bone.

Hayhurst et al., U.S. Pat. No. 5,037,422, issued Aug. 6, 1991, disclosesa bone anchor which comprises an elongated, thimble-shaped body havingslots extending lengthwise through the body and a suture receivingopening provided in the tip of the body. At least one ridge or barbextends outwardly from the exterior of the body and defines an edgewhich is adapted to be lodged in the wall of a bore formed in the bonemass. The tip of the anchor is configured to be inserted into a bore inthe bone, such that when tension is applied to the sutures, theresilient walls of the anchor are flared outwardly, locking the anchorinto the bore within the bone.

Paulos et al., U.S. Pat. No. 4,988,351, issued Jan. 29, 1991, disclosesa soft tissue washer for use with a bone screw for attaching soft tissueto a bone. The washer comprises a plurality of sharp pins extending fromthe distal face of the washer, there being a plurality of postsinterposed among the pins also extending from the distal face of thewasher. The washer comprises a central bore for receiving a bone screwtherewithin. As the bone screw is tightened into the bone, the sharppins engage the soft tissue to retain the tissue in intimate contactwith the bone; the posts limit the degree of penetration of the pinsinto the bone such that the distal face of the washer is maintained apredetermined distance from the bone surface, such that the soft tissueis maintained between the distal face of the washer and the bone.

Anspach Jr., U.S. Pat. No. 5,102,421, issued Apr. 7, 1992, discloses asuture anchor in the form of a rivet having three radially extendedflanges configured for penetration into a bone. A cylindrical extensionprojects rearwardly from the flanges and has a suture secured thereto. Aplurality of spiral grooves are formed within the flanges to facilitateturning of the ankle as it is tapped into a bone mass. Theaforementioned grooves also serve to define a series of serrationstherebetween, which serrations aid in preventing withdrawal of theanchor.

Other known devices attempt to dispose the suture anchor site whollywithin or underneath the bone surface, such as the "Quick Anchor" boneanchor manufactured by Mitek Surgical Products, Inc. of Norwood, Mass.The Mitek Quick Anchor bone anchor is configured to be dropped within abore of a bone mass using a collar device, functioning to retainexpandable wings in a retracted position during insertion. Once thedevice is inserted into the bone cavity, the wings expand, much like agrappling hook, to prevent withdrawal of the device. Presently knownsuture anchor devices are unsatisfactory in several respects. Forexample, the suture attachment sites of many known devices are of sharpor otherwise irregular construction, tending to irritate adjacenttissue. Moreover, many known devices tend to migrate within the bonemass, which may result in the device becoming lodged within a joint. Inaddition, presently known devices require cumbersome tools andaccessories for inserting the device, for example devices which requireturning or screwing during insertion.

A suture anchor is thus needed which overcomes the shortcomings of theprior art.

SUMMARY OF THE INVENTION

The present invention provides a suture anchor which addresses theshortcomings associated with the prior art.

In accordance with one aspect of the present invention, a bone isprovided which includes an elongated shaft having a flat head portionattached to a proximal end thereof. The head portion further comprises arounded cap or dome which functions as a suture anchor site. Duringinstallation, the surgeon drills an elongated bore into the bone mass,and presses the shaft portion of the bone anchor into the bore. Inaccordance with a further aspect of the present invention, the boreincludes a counterbore configured to receive the flat head portion ofthe anchor. The dome extending from the flat portion is suitablyconfigured with openings through which sutures may be threaded, suchthat the sutures are securely anchored to the bone by the anchor device.The sutures may then be attached to soft tissue in a conventionalmanner.

In accordance with a further aspect of the present invention, theelongated shaft portion of the anchor device comprises a plurality offrustroconical tines which, when tension is applied to the sutures, tendto flare outwardly, locking the anchor in place and preventing outwardmigration of the device. Inward migration of the device is precluded bythe engagement of the undersurface of the flat head portion of thedevice with the counterbore.

In accordance with yet a further aspect of the invention, the domeportion of the anchor device is suitably of integral construction withthe head portion of the device, resulting in superior pullout strengthof the device.

In accordance with yet a further aspect of the invention, the shaftportion of the anchor device comprises a plurality of lengthwise groovesextending along the length of the shaft resulting in a plurality ofarcuate, spaced-apart tines extending along the length of the shaft.These grooves provide sites for bony ongrowth, further preventing axialand rotational migration of the device within the bone.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The subject invention will be hereinafter described in conjunction withthe appended drawing figures, wherein like numerals designate likeelements, and:

FIG. 1 is a schematic view of an anatomically normal human heel boneshowing soft tissue properly attached to the bone;

FIG. 2A is a schematic diagram of an exemplary flat bone anchor siteshowing soft tissue detached from the bone;

FIG. 2B is a schematic diagram of the bone anchor site of FIG. 2A shownprepared for receiving the bone anchor of the present invention;

FIG. 2C shows the bone anchor site of FIGS. 2A and 2B showing thesubject bone anchor in situ, maintaining the reattached soft tissue inintimate contact with the bone;

FIG. 3 is a side elevational view of an exemplary embodiment of the boneanchor device in accordance with the present invention;

FIG. 4 is a cross-section view of the bone anchor device of FIG. 3 takenalong line IV--IV of FIG. 3;

FIG. 5 is a cross-section view of the head portion of the bone anchordevice of FIGS. 3 and 4; and

FIG. 6 is an end view of the anchor shown in FIG. 4, taken along lineVI--VI of FIG. 4;

FIG. 7 is a first view of an alternate embodiment of an exemplaryanchor;

FIG. 8 shows the anchor of FIG. 7 rotated 90 degrees;

FIG. 9 is a top view of the anchor shown in FIGS. 7 and 8;

FIG. 10 is a side elevation view of an exemplary embodiment of a drivingtool in accordance with the present invention;

FIG. 11 is a cross-section view of the driving head shown in FIG. 10taken along lines XI--XI of FIG. 10;

FIG. 12 is an alternate thread configuration useful in the subjectanchors; and

FIG. 13 is a further alternate thread configuration using in accordancewith the present invention.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

Referring now to FIG. 1, a ligament 12 extends between a human tibia 16and a human calcaneus bone (heel bone) 10 in an anatomically normalankle joint. Ligament 12 is attached to tibia 16 at an attachment site18, and attached to calcaneus 10 at an attachment site 14. Althoughattachment sites 14 and 18 appear to form an arcuate line in FIG. 1,those skilled in art will appreciate that soft tissues such as ligament12 typically adheres to a bone over an irregular region which, forpurposes of this discussion, is approximated by the arcuate attachmentsite shown in the Figure.

When soft tissue such as ligament 12 becomes detached from the bone, forexample, as a result of an athletic injury or the like, it is oftendesirable to reattach the soft tissue to the bone. In this regard, ithas become common practice to grasp the free (detached) end of thetissue with sutures, and to securely anchor the sutures to the boneproximate the reattachment site. If desired, the adjacent joint may beimmobilized for a period of time to permit reattachment. With the softtissue held in intimate contact with the bone, the tissue will naturallygrew back into the bone surface, firmly reattaching itself to the bonein a relatively short period of time. For example, soft tissue 12 maybegin reattaching itself to calcaneus 10 in a matter of twenty-one days,and will be substantially reattached to the point that the patient maywalk on the ankle joint in as little as eight weeks. After approximatelysixteen weeks, the reattachment process is substantially completed.

The natural physiological process whereby the soft tissue grows backinto the bone occurs relatively quickly; hence, the useful life of thebone anchor device used to attach the suture to the bone proximate thereattachment site is thus on the order of sixteen weeks. However,because removal of the anchor device may require destruction of at leasta portion of the reattached tissue, it is often desirable to simplypermit the suture anchor to remain within the bone permanently. Thatbeing the case, it is highly desirable that the suture anchor exhibit ahigh pullout strength during the early stages of reattachment, and toexhibit a high resistance to migration thereafter. In addition, inasmuchas the suture anchor typically remains in situ permanently, it isdesirable that the suture anchor be minimally intrusive; that is, thesuture anchor advantageously comprises smooth, anatomically compatiblesurfaces exposed to adjacent tissue and bony structure.

Referring now to FIGS. 2A-2C, an exemplary soft tissue reattachment site21 suitably comprises a bone 20 (for example analogous to calcaneus 10)and soft tissue 26 (for example analogous to ligament 12) which hasbecome detached from bone 20. Those skilled in the art will appreciatethat the structure of bone tissue is generally either compact, corticalbone, i.e., the hard, dense, outside layer of bone, or spongy (alsoreferred to herein as cancellous bone), which contains many smallcavities which may be filled with marrow. Moreover, bones are alsogenerally classified according to their shape; that is, bones are eitherlong (as in the bones of the extremities), short (for example, bones ofthe wrist, ankle, and sesamoid bones), or flat (such as bones of thecranium, scapula, and ribs). In addition, certain bones, for examplebones of the vertebrae, are classified as irregular.

With continued reference to FIG. 2A, bone 20 may comprise a flat bonehaving an outer layer 22 of compact bone enclosing an inner-region 24 ofcancellous bone.

Referring now to FIG. 2B, reattachment site 21 may be suitably preparedfor reattachment of soft tissue 26 (not shown in FIG. 2B for clarity),by forming a bore 28 extending through outer layer 22 and into thecancellous portion 24 of bone 20. With momentary reference to FIG. 2C,an exemplary suture anchor device 40 may then be inserted into bore 28to maintain soft tissue 26 in intimate contact with bone 20 to permitthe soft tissue to naturally reattach itself to the bone.

Referring now to FIG. 3, suture anchor 40 suitably comprises a shaftportion 44, a head portion 42, and a neck portion 54 interposedtherebetween. Neck portion 54 is suitably integral with head portion 42,and in a preferred exemplary embodiment, is substantially cylindrical inshape.

Head portion 42 suitably comprises a disc portion 43 and a dome 66extending therefrom. Dome 66 advantageously includes one or more suturetunnels 68, as described in greater detail below in conjunction withFIGS. 5 and 6.

Disc portion 43 further comprises a substantially flat, annular,undersurface 56 and a substantially flat, annular upper surface 60separated by a circumferential land 58. In accordance with a preferredexemplary embodiment, disc portion 43 suitably comprises a first beveledsurface 62 joining land 58 and upper surface 60, and a second bevelledsurface 64 joining land 58 and undersurface 56.

With continued reference to FIG. 3, shaft portion 44 suitably comprisesa plurality of frustroconical tines 46A-46F. In the illustratedembodiment, shaft portion 44 suitably comprises six (6) tine segments,namely, respective segments 46A-46F. However, any suitable number oftine portions may be employed in the context of the present invention,for example in the range of one to twelve or more, depending on theparticular bone mass within which the device is to be installed, andmost preferably on the order of four to eight tine portions.

In accordance with a further aspect of the invention, respective tineportions 46A-46F each comprise a flat annular surface 48 disposed in aplane substantially perpendicular to the longitudinal axis of anchor 40,an angled, frustroconical portion 52, and an arcuate junction 50defining the junction between flat portion 48 and angled portion 52.Shaft portion 44 suitably terminates at a flat, distal land 70.

With continued reference to FIG. 3 and as discussed in greater detailbelow in conjunction with FIG. 6, shaft portion 44 suitably comprisesone or more grooves 72 extending along the length of shaft portion 44.

More particularly and with reference to FIGS. 3 and 6, respectivegrooves 72A, 72B, and 72C are suitably spaced apart along shaft 44,forming respective tine sections 74A, 74B, and 74C. As best seen in FIG.3, each of respective tine sections 74A-74C comprises a portion ofrespective tine segments 46A-46F. Although respective grooves 72A-72Care substantially semicircular in cross section as shown in FIG. 6,virtually any geometry may be employed such that respective tinesections 74A-74C are spaced apart from one another. In this way, whenanchor 40 is installed within a bone mass, bony ingrowth may penetratethe interstices formed by respective grooves 72A-72C intermediate tinesegments 74A-74C. The presence of this bony ingrowth helps ensure thatanchor 40 remains stationary within the bony mass. In particular, thepresence of bony ingrowth within respective grooves 72A-72Csubstantially impedes rotational migration of anchor 40, as well assubstantially impeding axial migration (either into the bone or out ofthe bone) by enveloping the complex geometric structure comprising shaft44.

Referring now to FIGS. 4-6, the outer diameter of shaft 44 may besubstantially constant along its length in accordance with a firstembodiment of the invention (not shown). In the alternate preferredembodiment shown in FIG. 4, the outer diameter of the tines suitabledecreases, for example linearly, from tine segment 46A to tine segment46F.

More particularly, the diameter of shaft 44 may decrease along itslength approaching land 70, such that an included angle E defined by theconvergence of the shaft diameter is suitably on the order of 0-10degrees or more, and preferably in the range of 5-6 degrees, and mostpreferably on the order of six degrees. In the illustrated embodimentwherein each respective tine segment 46A-46F is suitably substantiallyequal in length, i.e., wherein each tine segment has an approximatelyequal axial dimension, the various angles defined by junction 50increase from tine segment 46A to tine segment 46F, that is, eachrespective land 48 corresponding to tine segments 46A-46F decreasesalong the length of shaft 44 (to the left in FIG. 4), each angledsegment 52 also decreases along the length of shaft 44, and the angledefined by junction 50 for each tine segment correspondingly increasesalong the length of shaft 44 (i.e, from right to left in FIG. 4). Inthis regard, while the respective angled junctions 50 corresponding tothe various tine segments are shown as a sharp corner in the drawingFigures, it may be advantageous from a manufacturing standpoint toinclude a small radius at junction 50 in lieu of a sharp corner.

With continued reference to FIG. 4, an internal angle R may also bedefined for each tine segment. Consistent with the foregoing discussion,the angle R for each tine segment will increase along the length ofshaft 44 (i.e., from right to left in FIG. 4).

In a preferred embodiment of the invention, an axial dimension, forexample, a common dimension for each respective tine segment 46A-46F,may be defined as shown in FIG. 4. In a particularly preferredembodiment, axial dimension for each tine segment is suitably on theorder of 0.025-0.040 inch, and most preferably on the order of about0.030 inch, such that the length of shaft 44 for the 6 tine embodimentshown in the Figures is on the order of approximately 0.180 inch. Inparticular, the length of shaft 44 is most desirably approximately 0.120inch for use in conjunction with small bones or for use with smallchildren, and may suitably be on the order of 0.240 inch for use inmiddle sized bones or in average sized people, and approximately 0.360inch for large bones and/or for use in larger individuals.

While any desired angle E may be employed in the context of the presentinvention, an angle on the order of five degrees facilitates convenientinsertion and self-alignment of anchor 40 into bore 28, as discussed ingreater detail below.

With continued reference to FIG. 2 and 4-6, a surgeon suitably preparesa reattachment site 21 in the following manner.

With particular reference to FIG. 2B, a bone drill (not shown) issuitably employed to introduce bore 28 in the bone site, which extendsthrough compact layer 22 and cancellous layer 24. The total length ofbore 28, i.e., from the outer surface of compact layer 22 until thebottom 29 of bore 28, is referred to in FIG. 2B as dimension 35. Withmomentary reference to FIG. 4, dimension 35 (FIG. 2B) corresponds todimension D of anchor 40, and is advantageously in the range of 0.20inch to 0.50 inch, and most preferably in the range of 0.33 inch to 0.45inch. In practice, it may be desirable for dimension 35 of bore 28 (FIG.2B) to exceed dimension D of anchor 40 (FIG. 4) by a small amount, forexample on the order of 0.001 to 0.020 inch. In this way, disc portion43 of head 42 is advantageously disposed beneath the surface of compactbone layer 22 when anchor 40 is installed.

With continued reference to FIG. 2B, a counterbore 30 is suitablycreated in compact layer 22, either by using the same drill employed tocreate bore 28 or by using a secondary tool in addition to or inconjunction with the drill used to create bore 28. In order to maintainproper alignment, counterbore 30 and bore 28 are desirably created usinga single tool (not shown). With momentary reference to FIGS. 2B, 3, and4, the axial dimension of counterbore 30 is suitably equal to orslightly greater than the thickness of disc 43 (corresponding todimension F in FIG. 4), and is suitably on the order of 0.020 to 0.50inch, and most preferably on the order of about 0.40 inch. The depth ofcounterbore 30 is limited by the thickness of compact bone layer 22 inthe vicinity of the reattachment site, and, hence, the size of anchor 40is advantageously selected in accordance with the physical dimensions ofthe reattachment site.

In any event, the depth of bore 28 should be selected so thatundersurface 56 of disc 43 engages corresponding surface 31 ofcounterbore 30; that is, while base 70 of device 40 should desirably beproximate base 29 of bore 28 when anchor 40 is installed, it is notnecessary that base 70 of device 40 contact base 29 of bore 28, whereasit is highly desirably that undersurface 56 of device 40 physicallyengage surface 31 of counterbore 30. In this way, inward axial migrationof anchor 40 will be substantially inhibited to the extent the integrityof compact bone layer 22 in the vicinity of counterbore 30 remainsintact.

The diameter of bore 28 should be selected to be equal to or slightlysmaller than the largest diameter of respective tine segments 46A-46F.More particularly, the diameter of bore 28, illustrated as dimension 32in FIG. 2B, is advantageously on the order of 0.010 to 0.040 (and mostpreferably on the order of 0.028 inch) smaller than dimension G (seeFIG. 4) of device 40. In this way, the various arcuate junctions 50corresponding to the tine segments will frictionally engage thecircumferential walls of bore 28 during insertion of anchor 40 intodevice 28. Depending on various physical characteristics of the materialcomprising anchor 40 as discussed in greater detail below, and furtherdepending on the hardness of the bone and the vicinity of reattachmentsite 21, and further depending on the physical dimensions of the varioustine segments in the vicinity of respective junctions 50, the frictionalengagement between shaft 44 and bore 28 may result in a deflection ofthe tine segments as the device is inserted into the bore, thedeflection of compact bone 22 and cancellous bone 24 proximate thedevice, or a combination of both. To the extent anchor 40 frictionallyengages the bone during insertion, the outward flaring of respectivetine segments 46A-46F (and particularly in the region of respectivearcuate junctions 50) with respect to the bone proximate thereto willinhibit outward axial migration of anchor 40.

Finally, the diameter of counterbore 30 should advantageously beapproximately equal to or slightly greater than the diameter of disc 43(dimension L in FIG. 4). In the preferred exemplary embodiment shown inthe drawing Figures, dimension L is suitably on the order of 0.020 to0.10 inch, and most particularly on the order of 0.040 to 0.075 inch,and most preferably on the order of about 0.0625 inch. Thus, thediameter of counterbore 30 should suitably be on the order of 0.000 to0.030 inch, and most preferably on the order of 0.020 inch, greater thandimension L to facilitate optimum seating of device 40 withincounterbore 30.

With continued reference to FIGS. 2B and 2C, after reattachment site 21is properly prepared by the surgeon, anchor 40 may be suitably insertedinto bore 28, for example by urging the device into the bore by pressureexerted by the surgeon's thumb or forefinger, or by tapping the devicewith a suitable impact tool. When anchor 40 is firmly seated within thebore, soft tissue 26 may be suitably secured to the attachment site withone or more sutures 36, as is known in the art. In this regard, sutures36 may be threaded through tunnel 68 prior to inserting anchor 40 intothe bore, after the anchor is partially seated within the bore, or uponfully seating the anchor within the bore.

More particularly and with reference to FIGS. 5 and 6, thecross-sectional area of tunnel 68 is suitably large enough toaccommodate one or more sutures extending through the tunnel. It is alsodesirable to ensure that sufficient material is present within dome 66to avoid breakage even as substantial tension is applied to the sutures,for example during attachment of the soft tissue. Moreover, thecross-sectional area of tunnel 68 should also be sufficient to permitstandard suture needles to conveniently pass through the tunnel, evenwhen device 40 is seated within a bone.

To facilitate the convenient threading of sutures through anchor 40 insitu, an included angle P associated with tunnel 68 may be defined,which is suitably on the order of 10-60 degrees, and preferably on theorder of 25-35 degrees, and most preferably about 30.6 degrees.Furthermore, the distance between the respective openings comprisingtunnel 68 may be conveniently defined as dimension Q (FIG. 6), suitablyon the order of 0.030 to 0.090 inch, and preferably on the order of0.050 to 0.075 inch, and most preferably about 0.060 inch. Finally, thediameter of tunnel 60 is suitably on the order of 0.020 to 0.060 inch,and most preferably about 0.045 inch.

Once anchor 40 is installed within the bone site, for example as shownin FIG. 2C, and soft tissue 26 is suitably reattached to the bone sitevia sutures 36, it is desirable to minimize irritation of soft tissue 26and surrounding tissue by device 40. In this regard, it is desirable toseat disc 43 within counterbore 30 to the extent permitted by theanatomical configuration of bone site 21. In addition, it is desirablethat the geometry of dome 66 be such as to minimize discomfortassociated with the contact between dome 66 and the adjacent anatomy.

More particularly, dome 66 is suitably highly polished, and exhibits asmooth, curved surface, for example a hyperbolic, ellipsoid, orsemispherical shape. In addition, the respective openings comprisingtunnel 68 may be radiused, bevelled, or otherwise configured to avoidsharp corners. In a particularly conferred embodiment, dome 66 suitablycomprises a substantially uniform radius on the order of 0.100 to 0.176inch, and most preferably on the order of 0.130 inch resulting in amaximum dimension C (FIG. 4) on the order of 0.020 to 0.070 inch, andmost preferably about 0.050 inch.

For reattachment sites such as that shown in FIG. 2, i.e., wherein asubstantially flat bone surface is available, disc 43 may besubstantially seated within counterbore 30. However, it may also bedesirable to employ anchor 40 at reattachment sites which are eitherconcave, convex or otherwise irregular. Accordingly, the diameter andthickness of disc 43, as well as various other dimensions of head 42 (inparticular the dome 66) may be configured to provide adequate materialstrength to avoid breakage as tension is applied to the sutures, whileat the same time providing smooth, nonabrasive and minimally invasivesurfaces to reduce irritation of surrounding tissue.

In accordance with a further aspect of the present invention, anchordevice 40 is advantageously made from any suitable biocompatiblematerial, for example titanium alloy, stainless steel, class six implantgrade plastic, and the like, or any other biocompatible material whichexhibits adequate pullout strength, sufficient strength to avoidbreakage as the sutures are pulled, and having sufficiently lowbrittleness to avoid breakage during long term usage of the device insitu. Alternatively, in view of the relatively short useful life ofdevice 40 (as discussed above), device 40 may be made from a suitablebioabsorbable material, for example, polyglycolic acid, a materialdistributed by Johnson & Johnson under the name ORTHOSORB™.

In accordance with a further aspect of the invention, shaft 44 and, ifdesired, neck portion 54 and at least underside 56 of disc 43 maysuitable exhibit a course finish to further promote bony ingrowth andthereby further stabilize anchor 40 against any degree of migration.

In accordance with a further aspect of the present invention, and withreference to FIGS. 7 to 9, the suture anchor 78 suitably comprises ashaft 90 and a head 80. Shaft 90 is suitably integral with head 80, andin a preferred exemplary embodiment, is substantially cylindrical inshape.

With particular reference to FIG. 7, shaft 90 further comprisesrespective major threads 94 and minor threads 92. As shown, preferablythreads 92 and 94 are interleaved and each suitably arranged in ahelical pattern. In addition, and with reference to FIG. 8, the distalend 96 of shaft 90 is preferably pointed for easy penetration andself-tapping into the bone matter. Preferably, distal end 96 is formedby tapering or angling of shaft 90, such as at an angle Q on the orderof about 30-45 degrees. The outermost point of distal end 96 ispreferably rounded, such as by being radiused on the on the order ofabout 0.010 inch. It should be appreciated, however, that alternativepre-tapping end configurations may be employed in the context of shaft90 and/or that conventional pre-tapping methodologies (e.g. pre-drillingand the like) may be employed as desired even with self-tappingconfigurations.

A preferred orientation of interleaved thread patterns 92, 94 is in aso-called "hi-low configuration". As will be appreciated by thoseskilled in the art, such a configuration includes minor threads having adimension of between about 60% to about 85%, and most preferably about75%, of the dimension of the major threads. Such a configuration withbone anchors is believed to offer advantages over other bone screwconfigurations because it allows for greater recruitment of bonematerial, and particularly of the soft cancellous bone matter, the partof the bone that the majority of the anchor fastens to. In addition,because only half of the threads have a large diameter, the amount oftorque required to set the anchor tends to be reduced.

Referring still to FIG. 7, in a preferred exemplary embodiment of theinvention, the spacing between either consecutive major threads 94 or ofconsecutive minor threads 92 is suitably on the order of 5-16 threadsper inch, and most preferably on the order of about 9 threads per inch.Thus, the spacing of the interleaved combination of major and minorthreads is suitably between about 10-32 threads per inch, and mostsuitably on the order of about 18 threads per inch.

In accordance with the preferred exemplary embodiment the diameter ofshaft 90, as illustrated by dimension C, is suitably on the order ofabout 0.040 to about 0.175 inch, and most preferably on the order ofabout 0.080 or 0.125 inch; the diameter of minor threads 92, asillustrated by dimension E measured from the central axis x of shaft 90to the outer edge of minor thread 92, is suitably on the order of about0.060 to about 0.255 inch, and most preferably on the order of about0.118 to 0.190 inch; and the diameter of major thread 94, as illustratedby dimension B measured from the central axis x of shaft 90 to the outeredge of thread 94, is suitably on the order of about 0.100 to about0.300 inch, and most preferably on the order of about 0.157 to 0.256inch.

The particular configuration and dimension of threads 92, 94 may varydepending on a variety of factors. For example, typically it isdesirable that the height and number of threads be chosen to optimizepull-out strength and minimize insertion torque as anchor 78 is workedinto the bone mass. Preferably, the height of minor thread 92 is betweenabout 25% to about 70% the height of thread 94, and more preferablyabout 50%.

While anchor 78 is shown as having an equal number of major threads 94and minor threads 92 per inch, it should be appreciated that the numberof threads per inch may vary as between the major and minor threadpatterns, or that vary over the length of anchor 78. For example, thenumber of threads per inch, while being the same for both major threads94 and minor threads 92 might be suitably varied over the length ofanchor 78, say for example with the pitch increasing from bottom 96 tothe top of shaft 90. That is, it may be desirable to have more threadsper lineal inch in one region along the axis of the shaft than in otherregions along the axis of the shaft. It is believed that such aconstruction may optimize the pull-out strength of anchor 78, while atthe same time desirably reducing the stress to the bony material uponinsertion of anchor 78.

Threads 92 and 94 are also suitably surface finished to minimize stresson the bony material as anchor 78 is inserted therein. In accordancewith a preferred embodiment of this aspect of the present invention, theouter surfaces or edges of threads 92, 94 are optimally rounded orsmoothed, for example to exhibit a radiused surface on the order ofabout 0.002 to about 0.005 inch. As will be appreciated by those skilledin the art, such finish can be engendered through electro-polishing,fine bead sanding or the like.

Referring now to FIG. 8, each of respective threads 92 and 94 preferablycomprise an angled helical upper surface 108, an angled helical undersurface 110, and a helical edge 112 interconnecting surfaces 108 and110. Preferably, surface 110 is downwardly angled from the outer edge ofthreads 92 and 94 to the body of shaft 90. This angle is illustrated bydimension N and, in a preferred embodiment, is typically about 25degrees. Similarly, upper surface 108 is preferably angled upwardly fromthe edge of threads 92, 94 to the body of shaft 90, as is illustrated bydimension O, typically about 5 degrees. The thickness P of the helicaledge 112 interconnecting upper surface 108 and lower surface 110 istypically about 0.005 inch.

With continued reference to FIG. 7, head 80 suitably comprises acurvalinear dome 82 and a substantially flat, annular undersurface 88separated by a circumferential segment 84. Head 80 preferably furtherincludes two oppositely facing grooves, e.g., semicircular grooves 102,102a and a suture tunnel 86, e.g., having a circular or ellipticalcross-section, passing through dome 82 such that tunnel 86 extendsbetween grooves 102, 102a. As will be discussed in greater detail below,a driving tool 120 (FIG. 10) suitably adapted to receive head 80 in suchway as to minimize the risk of driver slippage when torque is applied toanchor 78 is optimally utilized to set anchor 78 into a bone.

Head 80 is substantially superior to the prior art in that itscurvalinear shape minimizes the irritation of surrounding tissue whilealso minimizing the distance that head 80 protrudes above the bonymaterial. Furthermore, the configuration of head 80 adds additionalbenefit in that it impedes the migration of anchor 78 into the bonematerial and makes anchor 78 easily retrievable, a significant advancefrom the prior art.

Many times, anchors will be inserted so that the entire anchor imbedsbelow the cortical surface of the bone. After time, the bone will growover the anchor making it very difficult to retrieve. In this situation,a doctor must bore a hole into the bone and search for the buriedanchor. Because head 80 stays in the upper cortical surface of the bone,bony overgrowth will not likely cover head 80 and, thus, head 80 willnot likely be lost beneath the cortical surface.

With reference now to FIG. 9, segment 84 preferably is circular in shapesuitably exhibiting two substantially flat sides 100, 100a parallel totunnel 86. Cut or otherwise formed into sides 100, 100a are respectivegrooves 102, 102a. In a preferred embodiment of this aspect of theinvention, the dimension F between sides 100 and 100a is suitably on theorder of about 0.060 to about 0.240 inch, and most preferably on theorder of about 0.140 inch. The depth G of grooves 102, 102a is suitablyon the order of about 0.020 to about 0.080 inch, and most preferably onthe order of about 0.050 inch. The radius of grooves 102, 102a issuitably on the order of about 0.020 to about 0.080 inch, and mostpreferably on the order of 0.050 inch. It should be appreciated however,that grooves 102, 102a may be variously configured such as, for example,exhibiting a square, rectangular or other suitable configuration.

Arc segments 104, 104a of segment 84 are preferably curvalinear,optimally circular in nature. In a preferred exemplary embodiment,dimension I is suitably on the order of about 0.080 to about 0.250 inch,and most preferably on the order of about 0.157 inch.

Referring back to FIG. 7, dome 82 preferably consists of a smooth curvedsurface, e.g., a symmetrical sinusoidal shaped element having respectiveconnected inward and outward facing arcs. The radii of both arcs arepreferably equal and are illustrated as dimension J in FIG. 7.Preferably, dimension J is on the order of about 0.040 to about 0.100inch, and most preferably on the order of about 0.047 inch.

Preferably dome 82 is configured to possess an upper smooth curvalinearconfiguration. For example, as shown best in FIG. 8, dome 82 and segment84 combine to form the structure surrounding tunnel 86, and the distanceK from the top of dome 82 to underside 88 is suitably on the order ofabout 0.060 to about 0.120 inch, and most preferably on the order of0.080 inch. Preferably, head 80 is suitably dimensioned to ensure thatundersurface 88 seats against the outer surface of the bone into whichanchor 78 is inserted, while minimizing soft tissue irritation bysegment 84; for example, by configuring segment 84 to exhibit athickness L on the order of about 0.015 to about 0.040 inch, and morepreferably on the order of 0.022 inch.

It should be appreciated, however, that other anchor head configurationsmay be suitably utilized. For example, dome 82 and segment 84 could besuitably modified to maintain the general curvalinear configuration,while at the same time affording other benefits. In this regard, segment84 could be provided with one or more nibs or other protrusions (notshown) on underside 88 thereof to facilitate attaching of tendons or thelike between head 80 of anchor 78 and the bone into which it isinserted.

With reference now to FIGS. 7 and 9, a tunnel 86 is suitably configuredto pass completely through head 80 between parallel sides 100 and 100a.Preferably, tunnel 86 exhibits a cross-sectional area sufficiently largeenough to permit a standard suture needle to conveniently passtherethrough, particularly in the presence of one or more suturesextending therethrough. Tunnel 86 is a significant advancement over theprior art in that if a suture breaks while in anchor 78, a doctor canconveniently thread a new suture through hole 86. Previously, the anchorhad to be removed to insert a new suture. In accordance with a preferredembodiment of this aspect of the present invention, the tunnel 86exhibits a diameter on the order of about 0.040 to 0.100 inch, and morepreferably on the order of about 0.065 inch or 0.075 inch. Tunnel 86 issuitably positioned near underside 88. Preferably, the distance M froman axis passing through the center of tunnel 86 to underside 88 is onthe order of about 0.020 to about 0.050 inch, and more preferably on theorder of about 0.032 inch.

To minimize discomfort associated with the contact between head 80 andadjacent anatomy, the edges of head 80 and the respective openingscomprising tunnel 86 may be radiused, bevelled, or otherwise configuredto avoid sharp corners. This can be accomplished by any suitable manner,such as by machining, grinding, electro-polishing, fine bead blastingand the like. In particular, respective junctions 106 and 106a of tunnel86 (i.e., the tunnel openings) are preferably radiused to preventsutures passed through tunnel 86 from being snagged or severed by anysharp corners contained thereon. In a preferred embodiment of theinvention, the radius of edges 106, 106a is suitably on the order ofabout 0.004 inch.

Anchor 78 may be configured to exhibit any length A depending on thenature and type of bone it is intended to be used with. In accordancewith a preferred aspect of the present invention, anchor 78 exhibits alength on the order of about 0.125-1.5 inch, and most preferably on theorder of 0.472-0.551 inch.

Still referring to FIGS. 7 to 9, in a further embodiment of the presentinvention anchor 78 may be suitably configured with an axial bore 114extending through the entirety thereof. Bore 114 preferably exhibits adiameter R suitably on the order of about 0.020 to about 0.10 inch, andmore preferably on the order of about 0.030 to about 0.075 inch. Ingeneral, preferably the thickness of the walls of shaft 90 surroundingbore 114 are on the range of about 0.020 to about 0.10, more preferablyabout 0.025 inch.

Anchor 78 having bore 114 extending therethrough is, in accordance withthis aspect of the present invention, suitably configured to enable aguide wire to be advantageously passed through anchor 78 while in use.For example, in some circumstances, it may be desirable to pin softtissue to a bone before inserting a bone anchor. For example, if adoctor is fixing a tendon in a shoulder, he may want to pin the tendonin place before inserting the anchor. In this respect, once the tendonis lightly secured in place, the doctor may install a suitable guidewire into a desired position and slide anchor 78 with bore 114 over thewire for anchor position guidance. In this situation, when anchor 78 isinserted into the bone matter, head 80 advantageously will residedirectly on top of the soft tissue, securing the tissue betweenunderface 88 and the bone surface, thereby adding extra stability to thetissue/bone interface.

Because, in this configuration, head 80 operatively engages the softtissue, to aid in holding the tissue to the bone, a preferred embodimentof head 80 may include small teeth (nibs) on underside 88, or,alternatively, underside 88 may be concave in shape instead ofsubstantially flat. In addition to the configuration of head 80 inaccordance with this aspect, a doctor can also utilize sutures passedthrough tunnel 86 of head 80 to further secure the soft tissue in place.

In accordance with a further aspect of the invention, as shown in FIG.12, any suitable head configuration, e.g., domed head 80, as describedabove, can be used in conjunction with "pushtite" threads 142 whichcomprise a suitable helical screw thread pattern. Threads 142 areconfigured such that anchor 140 can be secured in the bone by pushing itinto a pre-tapped hole, and can be removed by unscrewing it. Thepreferred embodiment of anchor 140 differs from the tine configurationof anchor 40 in that anchor 140 can be advantageously backed out of thebone, while retaining the deflecting properties of the tines discussedabove in conjunction with FIGS. 3-6. Anchor 40, once inserted, tends tobe difficult to remove because tines tend to catch. With the embodimentshown in FIGS. 7-9 and in FIG. 12, to remove anchor 140, driving tool120 (FIG. 10) can be used in conjunction with head 80 to reverse it out.

In accordance with yet a further aspect of the invention, as shown inFIG. 13, a suitable head (e.g., head 80) can be used in conjunction with"twin lead" threads 152 which comprise a plurality of equal heightinterleaved helices. A benefit of anchor 150 is that it can be securedinto a pre-tapped hole in two revolutions, yet still provide anacceptable pull-out strength that is similar to other threaded anchors.

Referring now to FIGS. 10 and 11, driving tool 120 suitably comprises ahandle 122, a driving head 124, and a shaft 126 interposed therebetween.Driving head 124 is positioned at the distal end of shaft 126 andpreferably comprises a hollow cylindrical cavity 128. Respectiveoppositely displaced tabs 130 and 130a are suitably provided on theinside of cavity 128. Driving head 124 is suitably configured to fitover and/or engage head 80 of anchor 78 (see FIGS. 7 to 9) with tabs 130and 130a positioned to fit within grooves (notches) 102 and 102a in head80. In accordance with a preferred aspect of the invention, driving head124 may exhibit a depth sufficient to receive the entirety of head 80within. Typically the depth of driving head 124 will be slightly largerthan the height of head 80, and is suitably on the order of 0.065-0.125,and most preferably on the order of about 0.085 inch.

A further aspect of driving head 124 is that the inside wall 132 ofcylindrical cavity 128 is tapered inward such that when head 80 isinserted into driving head 124, head 80 wedges against inside wall 132,thus creating an interference or friction fit and securing head 80inside driving head 124. In addition, because head 80 is held insidecavity 128 by an interference or friction fit, head 80 will release fromcylindrical cavity 128 when pressure is reduced between the head and theinside wall (i.e., when the driving tool is pulled away from theanchor). The taper of inside wall 132 is shown by dimension W and mayvary depending on the dimensions of head 80; however, dimension W isgenerally on the order of about 5 degrees.

Because of this unique configuration, when anchor 78 is inserted intodriving tool 120, it will not fall out, allowing a doctor tostrategically place the anchor in hard to reach places without needingto hold the anchor with his other hand. In addition, this configurationcan make surgery safer and more efficient because it reduces the chancesof dropping the anchor inside the body.

Although the subject invention has been described herein in conjunctionwith the appended drawing Figures, those skilled in the art willappreciate that the scope of the invention is not so limited. Variousmodifications in the arrangement of the components discussed and thesteps described herein for using the subject device, may be made withoutdeparting from the spirit and scope of the invention as set forth in theappended claims.

We claim:
 1. A screw type bone anchor for attaching soft tissue to abone, comprising:a head having a central dome with a suture boreextending through the dome and a pair of substantially flat, oppositelydisposed lands configured about said dome, said lands being configuredfor engagement by a driving tool for inserting said anchor into thebones; and a shaft extending from said head, said shaft including afirst series of helical threads having a first diameter, and a secondseries of helical threads interleaved with said first series of threads,said second series of helical threads being characterized by a seconddiameter substantially different than said first diameter.
 2. The anchorof claim 1, wherein said suture bores configure to accommodate aplurality of sutures.
 3. The anchor of claim 1, wherein each of saidlands further comprises a groove configured to receive a correspondingtab of a driving tool.
 4. The anchor of claim 1, further comprising anaxial guide wire bore extending along the length of said anchor, suchthat a guide wire may be journaled through said guide wire bore.